The present invention relates to a novel humidity sensor and control apparatus useful therewith.
Humidity sensors are fundamentally based on the concept that changes in atmospheric moisture can cause dimensional changes in certain well known moisture sensitive materials such as cellulose, hair strands, animal horn and certain synthetic materials such as nylon. These dimensional changes are then converted by any of a variety of mechanical, electromechanical or pneumatic devices into a humidity reading or a control effect, as needed. Such devices are generally expensive to manufacture and very often are quite delicate to handle.
In the appliance industry there is a need for an inexpensive, rugged, humidity sensor that can be used to control the operation of the appliance for most energy efficient usage. For example, it is common practice in refrigerators to provide heaters in the breaker frames to raise the temperature of the surface adjacent the compartment opening to avoid moisture formation or sweating on the breaker frame. It is well known that sweating on refrigerator breaker frames tends to be a problem only in high humidity environments. As a result, a manual switch is provided to permit the appliance to turn off the anti-sweat heaters when they are not needed. The use of a humidity sensor to perform this control function automatically has long been considered, but a practical barrier to its adoption has been the cost and complexity involved in the use of known humidity sensors for this purpose.